struct X {};

template<typename T>
int foo(T n) {
   return n;
}

template<>
int foo<const X&>(const X& n) {
   return -1;
}

int main() {
   const X x;
   const X& rx = x;

   int n1 = foo(0); // OK
   int n2 = foo(rx); // ERROR:
   // In instantiation of 'int foo(T) [with T = X]':
   //error: cannot convert 'X' to 'int' in return

   return 0;
}

template<typename T>
int foo(T n) {
   return n;
}

template<typename T>
int foo(T n) {
   return n;
}

int foo(const X& n) {
   return -1;
}